Thermosetting resins with enhanced cure characteristics containing organofunctional silane moieties

ABSTRACT

A thermosetting resin. The resin includes a silane and a co-reactant monomer. The silane includes a quaternary silicon atom with first and second non-hydrolyzable moieties chemically bonded thereto. Each of the first and second non-hydrolyzable moieties includes respective first and second reactive groups. The reactive groups include at least one aromatic or unsaturated group having a triple bond.

Pursuant to 37 C.F.R. §1.78(c)(3), this application is a divisionalapplication claiming the benefit of and priority to prior filedco-pending application Ser. No. 13/748,730, filed Jan. 24, 2013. Thedisclosure of this previously filed application is expresslyincorporated herein by reference, in its entirety.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

FIELD OF THE INVENTION

The present invention relates generally to resins and, moreparticularly, to thermosetting resins.

BACKGROUND OF THE INVENTION

Thermosetting polymer materials are often used as adhesives andcomposite resins in applications that involve exposure to elevatedtemperatures. Therefore, there is an on-going need to improvethermo-chemical stability of cured resins in environments involving bothelevated temperature and exposure to chemical agents (such as oxygen,water vapor, and acid vapor). This on-going need has given rise to anumber of alternative materials that involve the cure of reactive groupssuch as cyanate esters, maleimides, benzoxazines, phthalonitriles, andaryl ethynyls. While these conventional resins are valued for their easeof use in affordable processes, such as resin transfer molding andfilament winding, and for offering maximum service temperatures that arehigher than those afforded by epoxy resins with similar processingcharacteristics, deficiencies remain.

For example, for conventional cyanate esters having more than about 3mmol cyanurate per cubic centimeter, the fraction of uncured reactivegroups is often larger than about 5% and, in fact, may be as much as20%. These uncured reactive groups become detrimental to the performanceof the thermoset polymer, e.g., unreactive cyanate esters may react withwater at elevated temperatures to release carbon dioxide gas, whichleads to blistering and mechanical failure of the resultant resin.

Some conventional approaches to combat the issues with uncured reactivegroups has been to increase the final cure temperature and/or toincrease catalyst level and activity; however, the former often requirestemperatures exceeding 300° C., which impose significant added costs tomany processing techniques while the latter is associated with decreasedthermal stability in wet environments. Still another approach adds alkylgroups and thereby decreases the thermo-chemical and thermo-oxidativestability of the resin. In fact, the decreased thermo-chemical stabilitylimits the maximum use temperature of such resins to values at least 50°C. lower than would otherwise be possible. Furthermore, the substantialmolecular volume increase associated with such alkyl chains decreasesthe density of cross-linkages within a network segment and lowers theglass transition temperature of the resin.

There remains a need for high-temperature thermosetting resins having aglass transition temperature exceeding 280° C., with a flexible moietyhaving a high level of thermo-oxidative resistance, and which minimallyadds to the molar volume of the network into which it is incorporated.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and othershortcomings, drawbacks, and challenges of conventional thermosettingresins by providing high thermal stability and minimally-adding to themolar volume of the network in which it is incorporated. While theinvention will be described in connection with certain embodiments, itwill be understood that the invention is not limited to theseembodiments. To the contrary, this invention includes all alternatives,modifications, and equivalents as may be included within the spirit andscope of the present invention.

According to one embodiment of the present invention, a thermosettingresin includes a silane and a co-reactant monomer. The silane includes aquaternary silicon atom with first and second non-hydrolyzable moietieschemically bonded thereto. Each of the first and second non-hydrolyzablemoieties includes respective first and second reactive groups. Thereactive groups include at least one aromatic or unsaturated grouphaving a triple bond.

According to some aspects of the present invention, the each reactivegroup is selected from a group consisting of cyanate ester, epoxide,episulfide, acrylate, alkene, styrenic, maleimide, phthalonitrile,acetylene, aryl ethynylene, benzoxazine, anthracene, aniline,trifluorovinyl ether, and perfluorocyclobutyl.

An embodiment of the present invention is directed to a method thatincludes curing non-hydrolyzable silanes to form a resin. Thenon-hydrolyzable silanes include a quaternary silicon atom and first andsecond terminal groups that are chemically bonded to the quaternaryatom. The first and second terminal groups each include at least onereactive group selected from the group includes at least one aromatic orunsaturated group having a triple bond. These at least one reactivegroups of the first and second terminal groups are configured to formmore than 3 mmoles of network junctions per cubic centimeter volume ofthe resin.

According to yet another embodiment of the present invention, athermosetting resin includes a plurality of non-hydrolyzable silanes,each having a quaternary silicon atom and four non-hydrolyzable terminalgroups chemically bonded thereto. At least two of the non-hydrolyzableterminal groups have a reactive group configured to form more than 3mmoles of network junctions per cubic centimeter volume of thethermosetting resin.

The above and other objects and advantages of the present inventionshall be made apparent from the accompanying drawings and thedescriptions thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention.

FIG. 1 illustrates a general, chemical formula for a reactive,non-hydrolyzable silane according to an embodiment of the presentinvention.

FIG. 2 illustrates a chemical structure for a reactive, non-hydrolyzablesilane according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating a method of synthesizing reactive,non-hydrolyzable silanes according to an embodiment of the presentinvention.

FIG. 4 illustrates a chemical structure for tris(4-benzyloxyphenyl)methylsilane, a first intermediate in the synthesis oftris(4-cyanatophenyl)methylsilane according to the synthesis provided inFIG. 3.

FIG. 5 illustrates a chemical structure fortris(4-hydroxyphenyl)methylsilane, a second intermediate in thesynthesis of tris(4-cyanatophenyl)methylsilane according to thesynthesis provided in FIG. 3.

FIG. 6 illustrates a chemical structure fortris(4-cyanatophenyl)methylsilane, a resin synthesized in accordancewith one embodiment of the present invention.

FIG. 7 illustrates a chemical structure fortetrakis(4-benzyloxyphenyl)silane, a first intermediate in the synthesisof tetrakis(4-cyanatophenyl)silane according to the synthesis providedin FIG. 3.

FIG. 8 illustrates a chemical structure fortetrakis(4-hydroxyphenyl)silane, a second intermediate in the synthesisof tetrakis(4-cyanatophenyl)silane according to the synthesis providedin FIG. 3.

FIG. 9 illustrates a chemical structure fortetrakis(4-cyanatophenyl)silane, a resin synthesized in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “chemical structure” and “chemical formula” refer tosymbolic products and processes involving symbolic manipulations ofspecific geometric arrangements of the representations or symbols ofatoms of a symbolic molecule. Comparatively, “chemical synthesis,”“chemical compound,” and “chemical substance” refer to a physicalprocess of manipulating atoms to form physically existing molecules andthe physical products formed by these physical processes. Other generalchemical terminology, such as “atom” and “reactive group” may beunderstood to refer to symbolic and physical entities, according to thecontext in which the terminology is used.

Turning now to the figures, and in particular to FIG. 1, a chemicalformula for a reactive, non-hydrolyzable silane 10 is shown according toone embodiment. The illustrated non-hydrolyzable silane 10 includesfirst and second reactive terminal groups (or moieties) E₁, E₂, firstand second non-reactive groups (or moieties) R₁, R₂, and a plurality oflinking groups L₁, L₂, L₃, L₄, wherein the elements comprising thereactive terminal groups E₁, E₂, the non-reactive groups R₁, R₂, and thelinking groups L₁, L₂, L₃, L₄ are selected from the group consisting ofhydrogen (H), carbon (C), nitrogen (N), oxygen (O), fluorine (F),silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), bromine (Br),and iodine (I). The terminal and linking groups are selected to benon-hydrolyzable, e.g., Si—O—C bond sequences or Si—X bond sequences,wherein X is a halogen, are avoided. Instead, the terminal and linkinggroups E₁, E₂, R₁, R₂, L₁, L₂, L₃, L₄ are selected such that, when theresultant resin is fully cured, a resultant resin network (an extendedmacromolecular network of cross-liked silanes) includes more than 3 mmolof junctions per cubic center of resin network, wherein networkjunctions include chemical structures having three or more linkages tothe resin network (not including any dangling terminal groups) connectedby a central unit of at least one, and generally less than 8, atoms,excluding hydrogen.

While the illustrated non-hydrolyzable silane 10 is shown with tworeactive terminal groups E₁, E₂, it should be readily apparent fromthose skilled artisans having the advantage of the disclosure providedherein, that silanes according to other embodiments of the presentinvention may comprise three or more reactive terminal groups and,optionally, one or more non-reactive terminal groups, one or morelinking groups, or both. Moreover, the architecture of reactive andnon-reactive terminal groups E₁, E₂, R₁, R₂ may be linear or branched.Reactive terminal groups E₁, E₂ may include one or more reactivefunctionalities as described in detail below. The linking groups L₁, L₂,L₃, L₄, if present, may be of any available architecture, including, forexample, cyclic structures bridging the terminal groups E₁, E₂, R₁, R₂.

The one or more reactive functionalities (i.e., reactive groups) of thereactive terminal groups E₁, E₂ are configured to enable the formationof the resin network having the plurality of network junctions, whichmay comprise three or more arms. For example, the one or morefunctionalities may include cyanate esters, epoxides, episulfides,acrylates, alkenes, styrenics, maleimides, phthalonitriles, acetylenes,aryl ethynylenes, benzoxazines, anthracenes, anilines, trifluorovinylethers, and perfluorocyclobutyl. The network forming reaction may beinitiated by heating (for example, to at least 70° C.), may occur in thepresence of a catalyst, or both.

Selection of the non-reactive terminal groups R₁, R₂ is such that totalmolar volume is minimized. Also, the selected non-reactive terminalgroups R₁, R₂ undergo less than about 5% weight loss when heated (rateof about 5° C./min in air) to temperatures of about 350° C. According toone embodiment of the present invention, and if two reactive terminalgroups E₁, E₂ per silane 10 are present, the molar volume of thenon-reactive terminal groups, R₁+R₂, is less than about 100 cc/mol, and,in some embodiments, is less than about 50 cc/mol. According to anotherembodiment of the present invention, and if three reactive terminalgroups E₁, E₂, E₃ are present, the mole fraction of the non-reactiveterminal group R₁ is less than 200 cc/mol. Suitable examples ofnon-reactive terminal groups R₁+R₂ may include, but are not limited to,methyls, phenyls, naphthyls, trimethylsilyls, trimethylsiloxies, andtrifluoromethyls.

The linking groups L₁, L₂, L₃, L₄ (referenced generally herein as L_(n),wherein n may any integer ranging from 0 to 4) are generally compact,may, in fact, be absent, generally will undergo less than about 5%weight loss when heated (rate of about 5° C./min in air) to temperaturesof about 350° C. In embodiments of the present invention having tworeactive terminal groups E₁, E₂, the combined molar volume of linkinggroups L_(n) may be less than about 150 cc/mol; in embodiments of thepresent invention having more than two reactive terminal groups E₁, E₂,E₃ (and optionally E₄) the combined molar volume of the linking groupsL_(n) may be less than about 300 cc/mol. Suitable examples of linkinggroups L_(n) may include, but are not limited to, dimethylsiloxies andmethylenes.

FIG. 2 illustrates a silane 12 according to one exemplary embodiment ofthe present invention, wherein chemical structures for groups E₁, E₂,L₁, L₂, L₃, L₄, R₁, R₂ are designated as follows: E₁, E₂, and E₃ arearyl cynante esters (E₃ replacing R₁), R₂ is a methyl, L₁ and L₃ aredimethylsiloxanes, and L₄ is absent.

Reactive, non-hydrolyzable silanes 10 according to various embodimentsof the present invention, and as compared to similar (or “analogous”)compounds having the central silicon atom replaced by a carbon atom in acorresponding chemical formula (not shown), obtain higher conversions(percentage of silane monomer cured) according to a pre-determinedschedule of times and temperatures. Bond lengths between the centralsilicon atom and the adjacent atoms of the terminal or linking groupsE₁, E₂, L₁, L₂, L₃, L₄, R₁, R₂ may range from about 180 pm to about 190pm (analogous carbon-centered compound bond lengths range from about 140pm to about 160 pm in length). Accordingly, an effective modulus ofelastic deformation of bonds between the central silicon atom andadjacent atoms is generally lower than an effective modulus of elasticdeformation of bonds between the central carbon atom and adjacent atomsin the analogous carbon-centered compound.

The lower elastic modulus afforded non-hydrolyzable silanes 10 accordingto embodiments of the present invention allows thermal fluctuationsacting on the central silicon atom and its adjacent atoms to produce agreater range of thermal motions. Additionally, the longer bond lengths,as compared to the analogous carbon-centered compound, provide greaterspacing between adjacent ones of the terminal and/or linking groups E₁,E₂, L₁, L₂, L₃, L₄, R₁, R₂. Altogether, the non-hydrolyzable silanes 10according to embodiments of the present invention have an increasedrange of motion, which enables the groups E₁, E₂, L₁, L₂, L₃, L₄, R₁, R₂to sample a greater range of geometric conformations at a giventemperature. Because successful formation of network junctions oftenrequires that the reactive groups exist within a narrow range ofgeometric conformations, the probability of reaching a geometricconformation suitable for network junction formation within a givenlength of time increases, as does the number of successful networkjunction formation events per unit time.

Relative rates of forward and reverse reactions in a reversiblenetwork-forming cross-linking reaction depend on a difference in energybetween the cross-linked network (i.e., the product) and the initial,non-cross-linked monomers (i.e., the reactants) and in accordance withclassical thermodynamic energy relationships. More specifically, thelower the energy of the product as compared to the energy of thereactants, the higher the relative rate of the forward reaction and,resultantly, the higher the concentration of products at equilibrium.The reverse also holds and results in a higher concentration ofreactants. The energy level of the products and reactants includes, atleast in part, an elastic energy component that depends on the geometricdistortion (here, geometric distortion of the terminal or linking groupsE₁, E₂, L₁, L₂, L₃, L₄, R₁, R₂). Geometric distortions tend to increasethe internal elastic energy of the product and may be somewhatproportional to a modulus of elastic deformation adjoining adjacentatoms. Thus, reactants having bonds of lower moduli of elasticdeformation reduces the energy associated with geometric distortion andminimizes the internal elastic energy of the network (product). As aresult, the energy level of the network (product) relative to thenon-cross-linked monomers (reactants) is lowered, and, resultantly, ahigher concentration of cross-liked network relative to non-cross-linkedmonomer (i.e., a higher conversion level) may be realized.

Reactive, non-hydrolyzable silanes 10 according to various embodimentsof the present invention also provide high densities of networkjunctions. Generally, a strong positive correlation exists between thenumber of network junctions (per unit volume) and key physicalproperties of resins, such as dry and wet glass transition temperatures.However, the nature of these relationships depends on the specificarchitecture of the network junctions. For example, the network junctiondensity of a resin cured by the cyclotrimerization of tricyanate estersfeaturing a single branch point in the monomer backbone serving as anetwork junction may be 3 mmol/cc, which corresponds to a dry glasstransition temperature at full cure of at least 250° C. The networkjunction density of a cured dicyanate ester system having no branchpoints serving as network junctions once cyclotrimerization takes placemay be at least 3 mmol/cc, which corresponds to a dry glass transitiontemperature at full cure of at least 280° C.

In those embodiments of the present invention wherein the centralsilicon atom is chemically bonded to three or four reactive groups E₁,E₂, E₃ (and optionally, E₄), there may be a minimal increase in volumeand in thermo-oxidative stability as compared to the analogouscarbon-centered compound. Other arrangements of flexible chemical bonds,such as propylene or cyclohexyl bridges may impart similar benefits butrequire a relatively greater volume, may decrease the dry glasstransition temperature, and may reduce thermo-oxidative stability.Although improvements in thermo-oxidative stability and hydrophobicityare well-known attributes of silane functionality, the simultaneous cureenhancing capabilities represent an unexpected discovery.

With reference now to FIG. 3, a flowchart 14 illustrating a method offorming a reactive, non-hydrolyzable silane according to one embodimentof the present invention includes mixing equimolar parts of4-bromophenyl benzyl ether and n-butyllithium (N-BuLi) intetrahydrofuran, which is chilled to about −78° C. (Block 16). After thechilled mixture reacts, with stirring, the mixture is slowly treatedwith silane at a ratio of 1 mole silane to 3 moles n-butyllithium (Block18). A first intermediate may be worked up (Block 20), by, for example,removing the cooling bath, removing solvents under pressure, andremoving LiCl salt by the addition of chloroform. The first intermediatemay also be precipitated into methanol and dried under nitrogen.

The first intermediate may be dissolved in a THF solution containing acatalyst, for example, palladium on carbon for hydrogenation (Block 22).Accordingly, the solution may be placed in a pressure safe vesseloperably coupled to a hydrogenator and pressurized (Block 24). A secondintermediate may be worked up (Block 26) which may include filtering outthe catalyst and removing the solvent under reduced pressure. The secondintermediate may also be purified by dissolution in THF, precipitatedout in hexane, washed in ether, and dried under vacuum.

Reactive groups may be added to the silane (Block 30) by dissolving thesecond intermediate in a chilled ether solution of cyanogens bromide.The solution may be treated with triethylamine in a drop-wise manner,with diethyl ether, and filtered to remove hydrobromide salt. Theorganic layer may be washed with de-ionized water and a brine wash anddried over magnesium sulfate. A product crystalline may be worked up(Block 32) by precipitation out from ether.

Network-forming reaction of the product crystalline may be initiated byheat, for example, to at least 70° C. and may occur in the presence of acatalyst.

If desired, and as would be evident to those skilled in the art havingthe benefit of the disclosure provided herein, reactive,non-hydrolyzable silanes according to some embodiments of the presentinvention may further include additive material components. For example,and although not shown, reactive, non-hydrolyzable silanes may beco-reacted with other monomers lacking a central silicon atom so as totailor the cure characteristics and other physical properties of theresulting resins. The co-reactant may be of the same type as thereactive, non-hydrolyzable silanes, although this is not required.Monomers of the co-reactant may react with other like monomers and notwith the reactive, non-hydrolyzable silanes so as to forminterpenetrating networks rather than co-polymerized networks. Accordingto other embodiments, the monomers of the co-reactant may be at leastpartially reactive with the reactive, non-hydrolyzable silanes so as toform partly interpenetrating and partly co-polymerized networks.

For instance, according to one embodiment of the present invention,tris(4-cyanatophenyl)methylsilane may be co-polymerized with up to 10 wt% of an epoxy monomer (such as the diglycidyl ether of bisphenol A) toform a co-polymerized network. In other embodiments of the presentinvention, the epoxy monomer may be polymerized after being mixed withan equal weight of bis(4-phenylethynyl)phenyl ether, following which,the mixture may be gelled by reaction of the cyanate ester groups. Onexposure to higher temperatures, entrapped phenylethynyl groups mayundergo a separate cross-linking reaction to form an interpenetratingnetwork.

Reactive, non-hydrolyzable silanes according to embodiments of thepresent invention may be used in systems containing insoluble fillerparticles and, more particularly, in systems containing dispersednanoparticles, reinforcements, or other additives configured to impartmechanical, thermal, moisture-resistant, and/or electricalcharacteristics. Features of reactive, non-hydrolyzable silanes, asdescribed herein, may remain largely unaltered by the addition of suchmaterials so long as such materials do not interfere with surfaceorganic reactive groups. The addition of filler particles may be useful,for example, as adhesives, sealants, composite resins, encapsulants,structures, and coatings.

The following examples illustrate particular properties and advantagesof some of the embodiments of the present invention. Furthermore, theseare examples of reduction to practice of the present invention andconfirmation that the principles described in the present invention aretherefore valid but should not be construed as in any way limiting thescope of the invention.

EXAMPLE 1

All manipulations of compounds and solvents were carried out usingstandard Schlenk line techniques. Tetrahydrofuran (THF), ether,chloroform, hexane, and toluene were dried by passage through columns ofactivated alumina under a nitrogen atmosphere and degassed prior to use.Anhydrous grade dichloromethane, acetone solvents, cyanogen bromide,n-butyllithium, and 10% palladium on carbon (wet, Degussa type)(Sigma-Aldrich Corp., St. Lois, Mo.) were used as received.Trichloromethylsilane and tetrachlorosilane (Gelest Inc., Morrisville,Pa.) and triethylamine (Sigma-Aldrich Corp.) were distilled prior touse. 4-benzyloxybromobenzene (Sigma-Aldrich Corp.) was recrystallizedfrom ether prior to use.

With reference now to FIG. 4, tris(4-benzyloxyphenyl)methylsilane 34 wasprepared by chilling a solution of 400 mL THF and 4-bromophenyl benzylether (20.00 g, 76.0 mmol was treated with 2.5M n-BuLi (30.4 mL, 76mmol)) to −78° C. for 2 hr while stirring. The reacted solution, nowheterogeneous, was treated with a slow addition of trichloromethylsilane(3.787 g, 25.33 mmol diluted with THF) and the cooling bath removed. Themixture reacted, while stirring and the solvents were removed underreduced pressure. Chloroform (300 mL) was added, the mixture stirred foran additional hour, and the mixture was filtered to remove LiCl salt.The solvent from the filtrate was removed under reduced pressure on arotary evaporator. The off-white crude product was precipitated intomethanol (400 mL), which was stirred overnight, filtered, and driedunder nitrogen to afford tris(4-benzyloxyphenyl)methylsilane 34 as awhite solid (13 g, 87% yield).

¹H, ¹³C, and ²⁹Si NMR measurements were performed ontris(4-benzyloxyphenyl)methylsilane 34 using a Bruker AC 300 or a Bruker400 MHz instrument (Bruker Corp., Billerica, Mass.). ¹H and ¹³C NMRchemical shifts are reported relative to the deuterated solvent peak(¹H, ¹³C: acetone-d6, δ 2.05 ppm, δ 29.9 ppm or CDCl₃, δ 7.28 ppm, δ77.23 ppm). ²⁹Si NMR chemical shifts are reported relative to externaltetramethylsilane at 0 ppm.

NMR assignments of the molecule shown in FIG. 4 include: ¹H NMR(acetone-d6) δ: 7.48 to 7.32 (m, 21H), 7.03 (d, J=8 Hz, 6H), 5.12 (s,6H), 0.75 (s, 3H). ¹³C NMR (acetone-d6) δ: 160.94 (C4), 138.32 (C6),137.47 (C2), 129.35 (C8), 128.70 (C1, C9), 128.50 (C7), 115.38 (C3),70.23 (C5), −2.66 (C10, SiCH₃). ²⁹Si NMR (acetone-d6) δ: −12.32 (s).

A THF (200 mL) solution containing tris(4-benzyloxyphenyl)methylsilane34 (10.00 g, 16.89 mmol) and 10 wt % palladium on carbon (400 mg) (e.g.,the catalyst), was placed in a 1000 mL pressure safe vessel equippedwith viton seals and, in turn, connected to a hydrogenator (ParrInstrument Co., Moline, Ill.). The vessel was pressurized with hydrogen(35 psi) and the solution was allowed to react with stirring for 48 hr.The catalyst was removed by filtration through celite, and the solventwas removed under reduced pressure to afford 4.60 g (85% yield) oftris(4-benzyloxyphenyl)methylsilane 36 (FIG. 5), as an off-white solid.For purification, tris(4-benzyloxyphenyl)methylsilane 36 was dissolvedin THF and precipitated out in hexane. The white product was filtered,washed with ether, and dried under dynamic vacuum. NMR assignments ofthe molecule shown FIG. 5 include: ¹H NMR (acetone-d6) δ: 8.47 (s, 3H),7.34 (d, J=8 Hz, 6H), 6.87 (d, J=8 Hz, 6H), 0.70 (s, 3H). ¹³C NMR(acetone-d6) δ: 159.43 (C4), 137.52 (C2), 127.37 (C1), 115.92 (C3),−2.51 (C5, SiCH₃). ²⁹Si NMR (acetone-d6) δ: −12.57 (s).

A chilled (−20° C.) ether (200 mL) solution containingtris(4-hydroxyphenyl) methylsilane, tris(4-benzyloxyphenyl)methylsilane36 (FIG. 5) (4.0 g, 12.41 mmol), and cyanogen bromide (4.88 g, 46.53mmol) in THF was treated with triethylamine (4.71 g, 46.53 mmol) in adrop-wise manner. The mixture was allowed to react for 2 hr withstirring at −20° C. Diethyl ether (500 mL) was added to the reactionmixture and stirred overnight. The mixture was filtered to remove thehydrobromide salt, and the organic layer was washed with (2×100 mL)de-ionized water, washed with a brine wash, and dried over MgSO₄. Thesolvents were removed under reduced pressure, and the crude product (3.2g, 80% yield) was precipitated out from ether to afford 2.9 g (72%yield) of tris(4-cyanatophenyl)methylsilane 38 (FIG. 6) as white acrystalline solid (mp 118° C., as determined on a Q2000 DifferentialScanning calorimeter (DSC) (TA Instruments, New Castle, Del.) undernitrogen flowing at 50 mL/min, with 5 minutes for equilibration at themaximum and minimum temperatures). NMR assignments of the molecule shownFIG. 6 include: ¹H NMR (acetone-d6) δ: 7.74 (d, J=9 Hz, 6H), 7.48 (d,J=9 Hz, 6H), 0.98 (s, 3H). ¹³C NMR (acetone-d6) δ: 154.48 (C4), 137.37(C2), 134.11 (C1), 115.13 (C3), 108.20 (C6, OCN), −4.43 (C5, SiCH₃).²⁹Si NMR (acetone-d6) δ: −10.51 (s).

Elemental analyses were obtained from Atlantic Microlabs or performed onan EA2400 Series II combustion analyzer (PerkinElmer Inc., Waltham,Mass.). The combustion analysis for tris(4-cyanatophenyl)methylsilane 38found a % C, 66.48 (66.01); % H, 3.80 (3.68); and % N, 10.57 (10.68).

Using the estimates of molar volume provided by Jozef Bicerano,Prediction of Polymer Properties (Marcel Dekker, 3d ed., 2002), thedisclosure of which is incorporated herein by reference in its entirety,the molar volumes of the various portions of curedtris(4-cyanatophenyl)methylsilane 38 are determined as follows: centralSi atom (28 cc/mol); methyl group (17 cc/mol); and phenyl cyanate ester(98 cc/mol). The central Si atom is expected to add just 23 cc/mol tothe total network volume and rigid bonds connected to the terminalcyanate ester groups are replaced with more flexible bonds. Based on theBicerano method, the density of cured tris(4-cyanatophenyl)methylsilane38 is expected to be 1.17 g/cc, while that of the carbon analog isexpected to be 1.21 g/cc.

In order to determine the density of curedtris(4-cyanatophenyl)methylsilane 38, the synthesized powder was melted,degassed at 150° C. for 30 minutes at 300 mm Hg, and poured into cleancylindrical silicone molds, which were preheated to 150° C. The curecycle was about 1 hour at 150° C. followed by 24 hours at 210° C. undernitrogen. Ramp rates between the long dwells were about 5° C./min. Thesilicone molds were such that cylindrically-shaped disc specimensmeasuring 12 mm in diameter by 3 mm thick were produced.

The resultant specimens were good quality discs and free of voids. Discsof the cured cyanate ester were placed into a vessel with two solutionsof CaCl₂ (dihydrate) in deionized water, at different knownconcentrations. The cured cyanate ester and dihydrate were combineduntil a neutrally buoyant solution was realized.

The density of the neutral solution was obtained by weighing a 10.00 mLvolumetric flask containing the fluid. This value was compared to theexpected density of a CaCl₂ solution at the known concentration andambient conditions. The measured density was 1.25 g/cc. By comparison,the density of a carbon-containing analog,1,1,1-tris(4-cyanatophenyl)ethane (commercially-available as ESR255),was determined to be 1.27 g/cc by the same method. These experimentalvalues are about 5% higher than the theoretically-obtained value and,therefore, indicate that the molar volumes of the molecular componentsare likely to be about 5% smaller than calculated. While not bound bytheory, such a discrepancy is believed to have a significant effect onlyon the estimated molar volume of the phenyl cyanate esters, with a valueof 91 cc/mol best satisfying the experimental data for both compounds.Further, it is believed that the substitution of silicon adds about 18cc/mol to the total volume of the network. The fully curedtris(4-cyanatophenyl)methylsilane 38 is expected to have about 3.15 mmolcyanurate per cubic centimeter volume of the resin, and because thetri-functional silicon atom also serves as a physical cross-link, about6.3 mmol cross-links per cubic centimeter are expected to be present inthe fully cured network. The expected, fully cured glass transitiontemperature of the network is above 300° C.

EXAMPLE 2

Tetrakis(4-benzyloxyphenyl)silane 40 (FIG. 7) was prepared by chilling asolution of 400 mL THF and 4-bromophenyl benzyl ether (20.00 g, 76.0mmol was treated with 2.5M n-BuLi (30.4 mL, 76 mmol)) to −78° C. for 2hr while stirring. The reacted solution, now heterogeneous, was treatedwith a slow addition of tetrachlorolsilane (3.22 g, 19 mmol diluted withTHF) and the cooling bath removed. The mixture was allowed to reflux at550° C., with stirring, for two nights. The solvents were removed underreduced pressure. Chloroform (300 mL) was added, the mixture stirred foran additional hour, and the mixture was filtered to remove LiCl salt.The solvent from the filtrate was removed under reduced pressure on arotary evaporator. The off-white crude product was precipitated intomethanol (400 mL), which was stirred overnight, filtered, and driedunder nitrogen to afford tetrakis(4-benzyloxyphenyl)silane 40 as a whitesolid (11 g, 76% yield).

¹H, ¹³C and ²⁹Si NMR measurements were performed on the white solidproduct using the Bruker AC 300 or the Bruker 400 MHz instrument (BrukerCorp.). ¹H and ¹³C NMR chemical shifts are reported relative to thedeuterated solvent peak (¹H, ¹³C: acetone-d6, δ 2.05 ppm, δ 29.9 ppm orCDCl₃, δ 7.28 ppm, δ 77.23 ppm). ²⁹Si NMR chemical shifts are reportedrelative to external tetramethylsilane at 0 ppm.

NMR assignments of tetrakis(4-benzyloxyphenyl)silane 40, as shown inFIG. 7, include: ¹H NMR (CDCl₃) δ: 7.54-7.38 (m, 28H), 7.05 (d, J=9 Hz,8H), 5.12 (s, 8H). ¹³C NMR (CDCl₃) δ: 160.54 (C4), 137.84 (C2), 136.98(C6), 128.66 (C8), 128.06 (C9), 127.59 (C7), 126.42 (C1), 114.46 (C3),69.80 (C5). ²⁹Si NMR (CDCl3) δ: −14.60 (s)

A THF (200 mL) solution containing tetrakis(4-benzyloxyphenyl)silane 40(10.00 g, 13.15 mmol) and 10 wt % palladium on carbon (400 mg) (e.g.,catalyst), was placed in the 1000 mL pressure safe vessel equipped withviton seals and, in turn, connected to the hydrogenator, as providedabove. The vessel was pressurized with hydrogen (35 psi) and thesolution was allowed to react with stirring for 48 hr. The catalyst wasremoved by filtration through celite, and the solvent was removed underreduced pressure to afford 4.80 g (91% yield) oftetrakis(4-hydroxyphenyl)silane 42 (FIG. 8) as an off-white solid. Forpurification, tetrakis(4-hydroxyphenyl)silane 42 was dissolved in THFand precipitated out in hexane. The white product was filtered, washedwith ether, and dried under dynamic vacuum. NMR assignments of themolecule shown in FIG. 8, include: ¹H NMR (acetone-d6) δ: 8.63 (s, 4H),7.38 (d, J=6 Hz, 8H), 6.81 (d, J=6 Hz, 8H). ¹³C NMR (acetone-d6) δ:159.54 (C4), 138.59 (C2), 125.98 (C1), 115.92 (C3). ²⁹Si NMR(acetone-d6) δ: −14.64 (s).

A chilled (−20° C.) ether (200 mL) solution containingtetrakis(4-hydroxyphenyl)silane 42 (4.0 g, 10 mmol), and cyanogenbromide (5.22 g, 50.mmol) in THF was treated with triethylamine (5.06 g,50 mmol) in a drop-wise manner. This mixture was allowed to react for 2hr with stirring at −20° C. Dichloromethane (200 mL) was added to thereaction mixture and stirred for an hour. The mixture was filtered toremove the hydrobromide salt, and the organic layer was washed with(2×100 mL) DI water, washed with a brine wash, and dried over MgSO₄. Thesolvents were removed under reduced pressure, and crude product (3.8 g,76% yield) was precipitated from ether to afford 3.5 g (72% yield) oftetrakis(4-cyanatophenyl)silane 44 (FIG. 9) as white crystalline solid(mp 169° C.). NMR assignments of tetrakis(4-cyanatophenyl)silane 44, asshown in FIG. 9, include: ¹H NMR (acetone-d6) δ: 7.77 (d, J=8, 8H), 7.54(d, J=8, 8H). ¹³C NMR (acetone-d6) δ: 155.73 (C4), 139.72 (C2), 132.38(C1), 116.40 (C3), 109.02 (C5, OCN). ²⁹Si NMR (acetone-d6) δ: −14.95(s).

Using the estimates of molar volume provided by Bicerano, as in theprevious example, the molar volumes of the various portions of curedtris(4-cyanatophenyl) methylsilane 44 may be determined as follows:central Si atom (28 cc/mol) and phenyl cyanate ester (98 cc/mol). Thecentral Si atom is expected to add just 23 cc/mol to the total networkvolume and four rigid bonds connected to the terminal cyanate estergroups are replaced with more flexible bonds. Based on the Biceranomethod, the density of cured tetrakis(4-cyanatophenyl)silane 44 isexpected to be 1.22 g/cc, while that of the carbon analog is expected tobe 1.25 g/cc. The fully cured density of Primaset® LECy (acommercially-available analog, Lonza Group Ltd., Basel, Switzerland) is1.23 g/cc. Therefore, co-cured blends of tetrakis(4-cyanatophenyl)silane44 with Primaset® LECy may be expected to have a very similar density.

In order to determine the density of curedtetrakis(4-cyanatophenyl)silane 44, equal weights oftetrakis(4-cyanatophenyl)silane 44 and Primaset® LECy, were combine,melted, and degassed at 150° C. for 30 minutes at 300 mm Hg. Blendingtetrakis(4-cyanatophenyl)silane 44 with Primasaet® LECy lowered themelting point (i.e., the melting point of the puretetrakis(4-cyanatophenyl)silane 44 was too high to afford a reasonablelevel of processability as a single-component resin). The samples werepoured into clean cylindrical silicone molds preheated to 150° C. Theco-cure cycle was about 1 hour at 150° C. followed by 24 hours at 210°C. under nitrogen. Ramp rates between the long dwells were about 5°C./min. The silicone molds were such that cylindrically-shaped discspecimens measuring 12 mm in diameter by 3 mm thick were produced.

The resultant specimens were good quality discs and free of voids. Discsof the co-cured cyanate ester were placed into a vessel and twosolutions of CaCl₂ (dihydrate) in deionized water, at different knownconcentrations. The cured cyanate ester and dehydrate were combineduntil a neutrally buoyant solution was realized.

The density of the neutral solution was obtained in the manner describedabove in Example 1. The measured density obtained by this method was1.26 g/cc. When the density of LECy is taken into consideration, theprojected density of the pure cured tetrakis(4-cyanatophenyl)silane 44would be 1.29 g/cc. As in Example 1, the experimental value was about 5%higher than the theoretically-obtained value and is consistent with avalue of 90 cc/mol for the molar volume of an aryl cyanate ester. Whilenot bound by theory, it is believed that the substitution of siliconadds less than 20 cc/mol to the total volume of the network, even thougha direct experimental comparison was not made. The fully curedtris(4-cyanatophenyl)methylsilane 44 was expected to have about 3.4 mmolcyanurate per cubic centimeter, and because the tetra-functional siliconatom also serves as a network junction upon cure, about 6.0 mmol networkjunctions per cubic centimeter are expected to be present in the fullycured network. For the co-network, the calculated number of cyanuratesand network junctions were 3.25 mmol/cc and 4.5 mmol/cc, respectively.The fully cured glass transition temperature for both the pure curedtetrakis(4-cyanatophenyl)silane 44 as well as its co-network with anequal weight of fully cured Primaset® LECytetrakis(4-cyanatophenyl)silane 44 are therefore expected to be wellabove 300° C.

EXAMPLE 3

The dry glass transition temperature for partially- or fully-curedcyanate ester resins is related to the extent of cure through thediBenedetto equation:

${\frac{T_{G} - T_{G\; 0}}{T_{G\;\infty}T_{G\; 0}} = \frac{\lambda\; a}{1 - {\left( {1 - \lambda} \right)a}}},$which is a monotonic, one-to-one function describing this relationshipquantitatively, and wherein T_(G), T_(G0), and T_(G∞) represent theglass transition temperatures of the partially-cured polymer, monomer,and fully-cured networks, respectively. The conversion factor, α,represents the fraction of monomer groups that have reacted, and λ is anadjustable parameter that typically takes on values ranging from about0.25 to about 0.45 for cyanate esters.

As a result, and for a given cyanate ester, the higher dry glasstransition temperature may be a reliable indication of a higher degreeof cure. Moreover, if the glass transition temperatures of uncuredmonomer and fully cured resin are available, the use of the diBenedettoequation may provide reliable approximations of the relative degree ofcure when comparing multiple resin systems on the basis of as-cured dryglass transition temperature values. In fact, even when a complete setof parameters for the diBenedetto equation is not known, the physicalmechanisms underlying the equation provide strong constraints on theunknown parameters and, thus, reliable approximations of the extent ofcure, may still be possible.

Cured resin samples were prepared by either melting thetris(4-cyanatophenyl)methylsilane 38 (FIG. 6) powder (Example 1) and/ormixing the tetrakis(4-cyanatophenyl)silane 44 (FIG. 9) powder (Example2) with Primaset® LECy liquid and melting the mixture at 150° C. under areduced pressure of 300 mm Hg for 30 minutes. The heated mixture waspoured into a reinforced silicone casting mold (12 mm diameter ×3 mmdiscs) and cured by heating in an oven under nitrogen to 150° C. for 1hour, 210° C. for 24 hours, and 150° C. prior to de-molding. Heatingramps were 5° C./min.

Thermomechanical analysis of cured samples was performed using a TA Q400thermomechanical analyzer (TMA) (TA Instruments) in dynamic (oscillatorycompression) TMA mode. Heating and cooling rates of 50° C./min wereused, and a program of heating to 350° C., cooling to 100° C., andre-heating to 350° C. (450° C. for the control sample ESR255) was used.A standard thermal cycling procedure, using limits of 0° C. and 200° C.,was used to determine and correct for the thermal lag caused by rapidheating rates. The mean compressive load on the samples was 0.1 N, withan oscillatory force applied at an amplitude of 0.1 N at a frequency of0.05 Hz.

Thermogravimetric analysis (TGA) was carried out using a TA Q5000 under60 mL/min of either nitrogen or air (TA Instruments). For TGA analysis,about 2 mg chips of the cured discs were heated at 10° C./min. to 600°C. Differential scanning calorimetry (DSC) was performed using a TA Q200DSC (TA Instruments) while heating about 5 mg of uncured resin from roomtemperature to 350° C., cooling to 100° C., and re-heating to 350° C.,all at 10° C. per minute for tetra(4-cyanatophenyl)silane 44 (FIG. 9).For tris(4-cyanatophenyl)methylsilane 38 (FIG. 6) and itscarbon-containing analog, ESR255, the DSC scans involved heating andcooling at 10° C./min to room temperature, heating to 120° C., coolingto −90° C., heating to 350° C., cooling to 100° C., and heating again to350° C., in sequence, so as to estimate the sub-ambient glass transitiontemperature of the uncured resin.

To estimate the heat capacity ratio factor in the diBenedetto equationfor ESR255, the DSC program involved heating at 10° C./min to 200° C.,holding for 5 min at 200° C., cooling at 10° C./min to 0° C., re-heatingat 10° C./min to 350° C. This method causes partial cure of the sampleand allows the DSC to measure the glass transition temperature and theextent of cure of the partially cured sample. The glass transitiontemperature, combined with the uncured and fully cured glass transitiontemperatures, enables experimental determination of the ratio.

Table 1 (below) provides the results of the DSC, TGA, and TMAexperiments and the derived diBenedetto parameters for the compoundstris(4-cyanatophenyl)methylsilane 38 (FIG. 6),tetrakis(4-cyanatophenyl)silane 44 (FIG. 9) and Primaset® LECy in equalproportions, and ESR255, i.e., 1,1,1-tris(4-cyanatophenyl)ethane, whichis the to tris(4-cyanatophenyl)methylsilane 38 carbon analog.

In the DSC experiment, a glass transition temperature of 123° C. wasdetermined for ESR255 that had a residual enthalpy of cure of 351 J/glower than the uncured sample (which showed 504 J/g enthalpy of cureusing the same baseline). Because full cure at 350° C. was notnecessarily obtained, the standard enthalpy of cure for cyanate esters(100 kJ/eq, or 866 J/g) was used to estimate conversion from thedecrease in residual enthalpy rather than the residual enthalpy itself.The resultant conversion was 41%, and the resultant value of the heatcapacity ratio, often abbreviated as λ, was 0.38. For cyanate esters, ingeneral, a reasonable range for values of this parameter is 0.25 to0.45.

As to ESR255, the data was sufficient to estimate the value ofconversion with confidence; however, for the other resins, only a rangecould be estimated from the following facts: the uncured glasstransition of cyanate esters generally ranges from at least −50° C. toabout 50° C.; the effect of silicon substitution is to lower the glasstransition temperature of a fully cured resin by at least 40° C.; alower glass transition temperature is accompanied by a correspondingincrease in the coefficient of thermal expansion (from Table 1, bothtris(4-cyanatophenyl)methylsilane 38 (FIG. 6) andtetrakis(4-cyanatophenyl)silane 44 (FIG. 9) exhibit a higher coefficientof thermal expansion than ESR255); and values for the diBenedettoparameter, λ, fall within the range 0.25-0.45 for analogous cyanateesters. Based on the relative coefficients of thermal expansion and thedata for analogous compounds, as well as the reported glass transitiontemperature of Primaset® LECy at full cure, the glass transitiontemperature of tris(4-cyanatophenyl) methylsilane 38 (FIG. 6) andtetrakis(4-cyanatophenyl)silane 44 (FIG. 9) would reasonably be expectedto be lower than that of ESR255. A minimum estimate of conversion wasobtained using the maximum values for uncured glass transitiontemperature, fully cured glass transition temperature, and λ.

TABLE 1 T_(G) T_(G) T_(G) CTE (DSC, (TMA, (TMA, (TMA, cured ConversionResin uncured) as-cured) fully cured) to 350° C.) (as-cured)tris(4-cyanato- −6° C. >350° C. >350° C. 56 92%-100% phenyl)methylsilanetetrakis(4-cyanato- <0° C. >350° C. >350° C. 56 92%-100%phenyl)silane/LECy 50/50 ESR255  6° C.  302° C.  419° C. 48 86%Conversions for tris(4-cyanatophenyl)methylsilane 38 (FIG. 6) andtetrakis(4-cyanatophenyl) silane 44 (FIG. 9) assume an uncured T_(G) ofnot more than −50° C. for the tetrakis(4-cyanatophenyl)silane 38 and,consequently, not more than 0° C. for a 50/50 mixture with Primaset®LECy. The fully cured T_(G) is no more than 419° C., and the heatcapacity ratio (X) in the diBenedetto equation ranges from about 0.25 toabout 0.45.

According to the data in Table 1, the conversion obtained underidentical cure conditions was higher for the silicon-containingcompounds than for the carbon-containing analog. Hence, substitution ofsilicon did result in improvements to processing because the failure toattain high conversions without recourse to temperatures well in excessof 250° C. is a known limitation of rigid cyanate esters, such asPrimaset® PT-30, that feature good thermo-oxidative stability. In thecase of the silicon-containing materials, TGA measurements showed thatthe 5% decomposition temperatures were 403° C. under nitrogen and 400°C. in air for tris(4-cyanatophenyl) methylsilane 38 (FIG. 6) and 408° C.under nitrogen and 400° C. in air for tetrakis(4-cyanatophenyl)silane 44(FIG. 9). Both resins retain adequate thermo-oxidative stability. Athigher temperatures, the presence of silicon enables the formation ofsilicon dioxide, which may play a further protective role. As expected,the glass transition temperature values were all well in excess of 300°C.

While the present invention has been illustrated by a description ofvarious embodiments, and while these embodiments have been described insome detail, they are not intended to restrict or in any way limit thescope of the appended claims to such detail. Additional advantages andmodifications will readily appear to those skilled in the art. Thevarious features of the invention may be used alone or in anycombination depending on the needs and preferences of the user. This hasbeen a description of the present invention, along with methods ofpracticing the present invention as currently known. However, theinvention itself should only be defined by the appended claims.

What is claimed is:
 1. A thermosetting resin comprising: a silanecomprising: a quaternary silicon atom; a first non-hydrolyzable moietybonded to the quaternary silicon atom and including a first reactivegroup; a second non-hydrolyzable moiety bonded to the quaternary siliconatom and including a second reactive group; a third non-hydrolyzablemoiety bonded to the quaternary silicon atom and including a thirdreactive group; and a fourth non-hydrolyzable moiety bonded to thequaternary silicon atom, wherein each of the first, second, and thirdreactive groups includes at least one triple bond and is selected fromthe group consisting of a cyanate ester and a phthalonitrile; and aco-reactant monomer configured to react and form a three dimensionalnetwork with the silane.
 2. The thermosetting resin of claim 1, whereinthe fourth non-hydrolyzable moiety is chemically inert.
 3. Thethermosetting resin of claim 1, wherein the silane further comprises: atleast one linking group between the quaternary silicon atom and one ormore of the first non-hydrolyzable moiety, the second non-hydrolyzablemoiety, and the third non-hydrolyzed moiety.
 4. The thermosetting resinof claim 1, wherein the co-reactant monomer includes an epoxy monomer.5. The thermosetting resin of claim 1, wherein the fourthnon-hydrolyzable moiety is an aromatic or an unsaturated group having atriple bond.
 6. A method comprising: curing non-hydrolyzable silanes toform a resin, each non-hydrolyzable silane comprising: a quaternarysilicon atom; a first terminal group chemically bonded to the quaternarysilicon atom; a second terminal group chemically bonded to thequaternary silicon atom; a third terminal group chemically bonded to thequaternary silicon atom; and a fourth terminal group chemically bondedto the quaternary silicon atom, the fourth terminal group beingnonhydrolyzable, wherein each of the first, second, and third terminalgroups is non-hydrolyzable and includes at least one reactive grouphaving a triple bond and is selected from the group consisting of acyanate ester and a phthalonitrile, wherein the reactive groups of thefirst, second, and third terminal groups form more than 3 mmoles ofnetwork junctions per cubic centimeter volume within the resin.
 7. Themethod of claim 6, further comprising: introducing one or more additiveswhile curing the non-hydrolyzable silanes, the one or more additivesconfigured to impart a mechanical characteristic, a thermalcharacteristic, a moisture-resistant characteristic, an electricalcharacteristic, or two or more thereof to the resin.
 8. A thermosettingresin comprising: a plurality of non-hydrolyzable silanes, eachnon-hydrolyzable silane of the plurality comprising: a quaternarysilicon atom; and four non-hydrolyzable terminal groups chemicallybonded to the quaternary silicon atom, at least three of the fournon-hydrolyzable terminal groups having a reactive group including atleast one triple bond and is selected from the group consisting of acyanate ester and a phthalonitrile, wherein the cured resin includesmore than 3 mmoles of network junctions per cubic centimeter volume. 9.The thermosetting resin of claim 8, wherein the one non-hydrolyzableterminal group without the reactive group is chemically inert.
 10. Thethermosetting resin of claim 1, further comprising: at least one linkinggroup between the quaternary silicon atom and the fourthnon-hydrolyzable moiety.
 11. The thermosetting resin of claim 3, whereinthe at least one linking group comprises dimethylsiloxy or methylene.12. The thermosetting resin of claim 1, wherein the silane has achemical name of tetrakis(4-cyanatophenyl)silane.
 13. The thermosettingresin of claim 5, wherein the fourth non-hydrolyzable moiety is selectedfrom a group consisting of methyl, phenyl, napthyl, trimethylsilyl,trimethylsiloxy, and trifluoromethyl.
 14. The thermosetting resin ofclaim 10, wherein the at least one linking group comprisesdimethylsiloxy or methylene.
 15. The thermosetting resin of claim 13,wherein the fourth non-hydrolyzable moiety is methyl, and wherein thesilane has a chemical name of tris(4-cyanatophenyl)methylsilane.
 16. Thethermosetting resin of claim 8, further comprising: at least one linkinggroup between the quaternary silicon atom and at least one of the fournon-hydrolyzable terminal groups.
 17. The thermosetting resin of claim16, wherein the at least one linking group comprises dimethylsiloxy ormethylene.